1. Field of the Invention
The present invention relates generally to photovoltaic systems. The present invention relates more particularly to photovoltaic roofing systems in which photovoltaic elements are integrated on a roof deck with conventional roofing materials.
2. Summary of the Related Art
The search for alternative sources of energy has been motivated by at least two factors. First, fossil fuels have become increasingly expensive due to increasing scarcity and unrest in areas rich in petroleum deposits. Second, there exists overwhelming concern about the effects of the combustion of fossil fuels on the environment due to factors such as air pollution (from NOx, hydrocarbons and ozone) and global warming (from CO2). In recent years, research and development attention has focused on harvesting energy from natural environmental sources such as wind, flowing water, and the sun. Of the three, the sun appears to be the most widely useful energy source across the continental United States; most locales get enough sunshine to make solar energy feasible.
Accordingly, there are now available components that convert light energy into electrical energy. Such “photovoltaic cells” are often made from semiconductor-type materials such as doped silicon in either single crystalline, polycrystalline, or amorphous form. The use of photovoltaic cells on roofs is becoming increasingly common, especially as device performance has improved. They can be used to provide at least a significant fraction of the electrical energy needed for a building's overall function; or they can be used to power one or more particular devices, such as exterior lighting systems.
Accordingly, research and development attention has turned toward the development of photovoltaic products that are adapted to be installed on a roof. While photovoltaic elements have been in use for some time, they tend to be heavy and bulky, and aesthetically unfavorable when installed on a roof. Roofing products having photovoltaic cells integrated with roofing products such as shingles, shakes or tiles have been proposed. A plurality of such photovoltaic roofing elements (i.e., including photovoltaic media integrated with a roofing product) can be installed together on a roof, and electrically interconnected to form a photovoltaic roofing system that provides both environmental protection and photovoltaic power generation. These can be very advantageous, but can be difficult to install on steep surfaces, and can often result in incomplete coverage of the roof surface with photovoltaic power generation. Moreover, fabrication and installation and connection of a plurality of smaller photovoltaic roofing elements can in some circumstances be a very slow, tedious, and costly process. There remains a need for improved devices and methods for the integration of photovoltaic media onto roof decks together with conventional roofing materials.